This invention relates to communication systems. More particularly, and not by way of limitation, the invention is directed to a network node, method, and mobile terminal for providing voice calls to a mobile terminal operating in a packet-switched-only network.
Wireless networks today, such as second-generation (2G) GSM networks, third-generation (3G) networks, and Wireless Local Area Networks (WLANs) support Packet-Switched (PS) services and/or Circuit-Switched (CS) services. A user in a 2G or 3G network may use either CS services such as speech, or PS services such as Internet Access. The availability of CS and PS services also depends on the terminal. Some devices such as Laptop PC-cards are PS-only devices, while other devices such as older GSM phones without GPRS support are CS-only devices. A user in a PS-only network may use only PS services, although Voice-over-IP (VoIP) is emerging. New wireless networks such as Wimax support only PS and not CS. New standards for PS-only networks are also being investigated by the Third Generation Partnership Project (3GPP) in a feasibility study for System Architecture Evolution/Long Term Evolution (SAE/LTE). The SAE portion of this study is focused on a new core network, while the LTE portion of the study is focused on a new radio network.
General information regarding 2G and 3G networks may be found in the technical specification 3GPP TS 23.060, v.6.13.0. Further information about the Gs interface may be found in the technical specification 3GPP TS 29.018, v. 6.4.0. Further information about SAE/LTE networks may be found in the technical specification 3GPP TS 23.882, v. 1.2.3. Each of these technical specifications is hereby incorporated herein by reference.
Many users, however, prefer CS voice service because the quality of CS voice service is in many cases superior to PS voice quality. Operators may also prefer CS voice services because operators must heavily invest to provide VoIP services.
Some existing networks contain both a CS part and a PS part of the network. An interface known as the Gs interface provides co-ordination between a Mobile Switching Center/Visitor Location Register (MSC/VLR), which handles CS traffic in the CS part of the network, and a Serving GPRS Service Node (SGSN), which handles PS traffic in the PS part of the network. The Gs interface is used by the MSC/VLR for paging the mobile terminal for CS services, for exchanging location information between the CS part and the PS part, and for conveying some CS-related procedures through the SGSN. The Gs interface makes it possible for a mobile terminal supporting both CS and PS services to connect to both services via the PS domain. The Gs interface enables a mobile terminal using a combined CS and PS network to send some messages only to the PS part to save radio transmissions. The PS part then informs the CS part of needed information through signaling to ensure that both the CS and PS parts of the network have the same information about the mobile terminal.
When a mobile terminal is operating in a PS-only network, there are several reasons why the mobile terminal cannot receive CS voice calls. First, there is no mechanism for registering the mobile terminal with an MSC. Second, even if the mobile terminal was registered with an MSC/VLR, there is no signaling mechanism for forwarding paging messages from the MSC/VLR to the mobile terminal. Thus, the mobile terminal cannot be alerted when a CS voice call is incoming. Additionally, the mobile terminal itself lacks the functionality for using more than one radio technology at the same time. Although some high-end mobile terminals are capable of supporting more than one network technology, they cannot use more than one radio technology at the same time because battery consumption or interference issues make it technically impossible. Low-end terminals, where cost is an important issue, are often not designed with this capability due to cost constraints. Thus, the terminal is restricted to using either PS-only data services or CS-only voice services, but not both at the same time. Therefore, if the mobile user is using a PS-only data service, the user cannot receive any CS voice calls.
It should also be noted that networks providing both CS and PS services (such as GSM or WCDMA), generally have better coverage than PS-only networks (such as WLAN). However, PS-only networks generally offer higher bandwidths, perhaps even 100 times higher, than networks providing both CS and PS services. This higher bandwidth can be very useful for applications such as IPTV, video, downloading from the Internet, and the like. When a mobile terminal is using a PS service in a PS-only network, it is technically feasible to maintain the PS service when moving to a combined CS/PS network, if the two networks are operated by the same operator, and if the operator has chosen to implement the network in this way. In the combined CS/PS network, the same radio access technology is utilized for both CS and PS services, and the mobile terminal can receive CS voice calls while running the PS service. However, in most cases, some PS bandwidth capability will be lost. From the bandwidth perspective, it would be beneficial for the terminal to continue to use the PS-only network, but the drawback is that any incoming CS calls to the mobile terminal are lost.
What is needed in the art is a network node, method, and mobile terminal for providing voice calls to a mobile terminal that overcomes the disadvantages of the prior art. The present invention provides such a network node, method, and mobile terminal.